JERUSALEM, July 7 (Reuters) - A senior Israeli military officer denied on Monday that Israel had killed six Hamas militants in an air strike, saying the men died when explosives went off in a tunnel they had dug.

Lieutenant Colonel Peter Lerner told reporters Israel was preparing for a possible escalation in hostilities along the Gaza frontier and had called up several hundred reserve troops.

Lerner said daily rocket fire at Israel from Gaza by Hamas fighters meant that whereas last week Israel had previously sought a deescalation, "now the Israeli military is talking about preparedness for an escalation". (Writing by Allyn Fisher-Ilan; editing by Andrew Roche)